The present invention generally relates to devices for heating liquids, and more particularly to an electric blood warmer utilizing nucleate boiling and heating by film condensation at subatmospheric pressure characterized by accurate temperature control and very high heat transfer rates, capable of heating blood or other fluids for infusion from refrigerated storage temperature to physiologic temperature at flow rates varying from zero to those required for massive transfusion. The present invention also relates to a device for heating or thawing physiologic or other fluids at high heat transfer rates without the possibility of subjecting the heated fluid to locally excessive temperatures.
Blood is generally stored at a temperature near 4.degree. C. Prior to intravenously infusing refrigerated blood into the human body, it should be warmed to near physiologic temperature (32.degree. to 37.degree. C.) During massive transfusions flow rates of 160 milliliters per minute or more may be required.
1. Background--Cross-Reference to Related Applications
This Application is related to the following pending (now issued) patent application.
______________________________________ Appn. Number 07/132,193 Filing Date December 14, 1987 Applicant Allan P. Bakke Title Ribbon-Flow Cartridge-Type Dry Heat Blood Warmer ______________________________________
The above pending application was allowed and issued as follows, before submission of the present continuation-in-part application.
______________________________________ U.S. Pat. No. 4,847,470 Date of Issue July 11, 1989 Title Electric Blood Warmer Utilizing Metallic Ribbon Flow Cartridge and Low Thermal Mass Heating Units Inventor Allan P. Bakke ______________________________________
2. Background--Description of Prior Art
Various kinds of blood warmers presently exist. Most utilize a flexible plastic container or conduit for the blood being heated, such as plastic tubing immersed in a warm water bath or a plastic bag or pouch sandwiched between heating plates. Heating plates are usually electrical resistance heaters. Cold blood entering the warmer at a high flow rate would suggest higher heat transfer rates decreasing as an aliquot of blood approaches the outlet of the warmer. At low or zero flow rates, however, a high heating rate near the inlet overheats locally causing hemolytic destruction of erythrocytes.
The related U.S. Pat. No. 4,847,470 utilizes etched foil heaters with uniform heating rates, low thermal mass heating plates, and points out the potential benefits of multistage heating, which approaches the constant wall temperature heat transfer model.